Wind power is considered one of the cleanest, most environmentally friendly energy sources presently available, and wind turbines have gained increased attention in this regard. A modern wind turbine typically includes a tower, generator, gearbox, nacelle, and one or more rotor blades. The rotor blades capture kinetic energy from wind using known foil principles and transmit the kinetic energy through rotational energy to turn a shaft coupling the rotor blades to a gearbox, or if a gearbox is not used, directly to the generator. The generator then converts the mechanical energy to electrical energy that may be deployed to a utility grid.
During operation of a wind turbine, various components of the wind turbine are subjected to various loads due to the aerodynamic wind loads acting on the blade. The blade loading is dependent on the wind speed, tip speed ratio and/or pitch setting of the blade. Tip speed ratio is the ratio of the rotational velocity of the blade tip to wind speed. It can be desirable to adjust operation of the wind turbine based on signals indicative of tip speed ratio (e.g. various speed readings) to adjust loading of the rotor blades of the wind turbine and/or to increase energy production of the wind turbine.
To reduce rotor blade loading, various methods and apparatus have been developed to allow the rotor blades to shed a portion of the loads experienced thereby. Such methods and apparatus include, for example, pitching the rotor blades and/or reducing generator torque during operation. Accordingly, many wind turbines include a wind turbine controller that can operate the wind turbine in various ways based on the tip speed ratio wind turbine loading. For instance, under various operating conditions, the wind turbine can adjust the torque of a generator and/or the pitch angle of the rotor blades to adjust the tip speed ratio to meet a desired tip speed ratio setpoint to increase energy capture by the wind turbine.
The pitch angle of a rotor blade can be controlled, for instance, using a wind pitch adjustment motor. The wind pitch adjustment motor can be a direct current (DC) motor driven by a DC/DC converter. Typically, a wind pitch adjustment motor includes a DC source, a control circuit, an inverter bridge, and/or a DC bus capacitor bank having one or more capacitor devices. Due to the high capacitance of the capacitor bank, a pre-charging circuit can be used in conjunction with a bypass contactor to limit the magnitude of an inrush current into the capacitor bank.
Conventional pre-charge circuits can include high power resistors, positive temperature coefficient (PTC) thermistors, transformers, switching current sources, linear current sources, or other circuit configurations to limit the current applied to the capacitor bank. However, such pre-charging techniques can be inefficient, time-consuming, and/or difficult to implement.
Accordingly, there is a need for systems and methods of pre-charging a capacitor bank simple, efficient, and controllable manner.